It is known to make pressed hops by drying fresh hop strobiles, to comminute the dried hop strobiles (e.g. down to a particle size of from about 2 to 10 mm) and to press the dried and comminuted hop strobiles to form shaped bodies, such as cubes, slabs or pellets. The pressed shaped bodies may then be packaged in containers which are substantially gas-impermeable. Such containers are, for instance, metal cans, but preferably bags made of plastic or aluminium foils (the latter may also be coated with plastics). The containers are usually evacuated and subsequently filled with an inert gas or an inert gas mixture. An inert gas mixture which, for instance, contains about 1/3 carbon dioxide and 2/3 nitrogen, has been found to be particularly suitable. The containers, after having been filled with the gas, are closed, e.g. by heat sealing.
According to another alternative, the dried and comminuted hop strobiles may be first placed in a foil bag, and the foil bag is then evacuated and filled with an inert gas mixture. Finally, the foil bag containing the unpressed hops may be compressed.
As a result of the evacuation and filling of the containers with an inert gas or gas mixture, the storage life of the pressed hops is greatly increased, this being due to the fact that the valuable bitter substances are protected against the access of air. The most valuable bitter substances are the .alpha.-acid or the humulone, and the .beta.-acid or the lupulone which, by oxidation, are gradually converted into the less valuable .alpha.- and .beta.-soft resins and eventually into the corresponding hard resins.
The .alpha.- and .beta.-acids are highly unsaturated compounds which may polymerize by themselves, resulting in a certain resinification, even if the pressed hops are stored in an inert gas atmosphere. Furthermore, the foil bags are not absolutely gas-impermeable so that traces of oxygen may penetrate into the containers, resulting in an oxidation of the .alpha.- and .beta.-acids, especially after prolonged storage.
Furthermore, packaged pressed hops are advantageous over the unpressed hops because they require less space during storage. However, pressed hops have a certain disadvantage in that they disintegrate relatively slowly when they are added to the beer wort.